This R34 application seeks support to refine and test a clinical algorithm for identifying autism spectrum disorders (ASD) in adults receiving outpatient psychiatric care. Evidence suggests that adults with ASD are overrepresented and underdiagnosed among individuals receiving psychiatric care. Adults with ASD may be medicated for disorders they do not have with medications that are not effective for treating ASD. They also may benefit from ASD-specific interventions that they do not get because of inaccurate diagnosis. ASD diagnostic tools are lengthy, most are validated only in children, and they require considerable training to administer correctly. Therefore they are not feasible for use with adults in community mental health settings. To develop a screening strategy appropriate for this setting, we will build upon our prior work in inpatient settings by partnering with Horizon House, a large community mental health organization in Pennsylvania, to identify adults with ASD in their care. We then will refine and validate our algorithm for identifying ASD in adults presenting for psychiatric treatment. Our goal is to use items readily available to clinicians, in combination with a brief screening tool, to accurately identify ASD in adults in community mental health settings, which would then lead to further diagnostic assessment. The specific aims of the proposed study are to: 1) Estimate the prevalence of undiagnosed ASD in community outpatient settings~ 2) Compare clinical characteristics, treatment and assigned diagnoses of adults with ASD with those of adults with other psychiatric disorders~ and 3) Develop and test a brief tool for community mental health practice to screen for ASD in adults. To determine cases of ASD, Horizon House staff will complete the SRS and the Autism Spectrum Disorders in Adults Screening Questionnaire (a shorter instrument used in similar studies) for adult clients with whom they have in-person contact during a 6-month period (n H 2000). Researchers then will conduct, on a sample of 450 subjects stratified by SRS score: 1) chart reviews to extract information using a checklist comprising the characteristics found to discriminate between adults with ASD and other psychiatric disorders in prior studies (developmental history, neurological problems, substance use and criminal activity~ Appendix B)~ 2) structured clinical interviews using the Autism Diagnostic Observation Schedule, Module 4, and the Structured Clinical Interview for DSM Disorders~ and 3) family interviews, using the Social Communication Questionnaire, semi-structured questions about early development, and the modified Family Interview for Genetic Studies. Case conferences will be conducted for all subjects to make a final determination of ASD. Once case status is determined, subjects with and without ASD will be compared on all variables using receiver operating characteristic curves and decision tree analyses to determine the most parsimonious creening strategies. If successful, the proposed study will provide the first US estimates of ASD in an outpatient population and will greatly enhance community clinicians' ability to identify adults with ASD.